Prior art cartridge case closure plugs are typified by the plug disclosed in U.S. Pat. No. 2,045,004, to Vickers, which discloses a cylindrically shaped plug having a soft core material, such as coarsely ground cork having a low tensile strength, encompassed by an outer shell of granular material. The disadvantage of the plug of Vickers is that is requires a complex manufacturing process to both form the plug and join the inner core to the outer shell. In addition, the plug of Vickers is incompatible with charge assemblies used with projectiles containing guidance elements or other impact sensitive elements.
Additional prior art cartridge case closure plugs are disclosed by U.S. Pat. Nos. 2,947,254, to Weiss, and 2,959,130, to Weiss et al. Both of the plugs disclosed by the patents of Weiss and Weiss et al are constructed of a plastic material, such as phenolic resin or other thermo-setting resins, reinforced with wood pulp, paper pulp, kraft pulp or chopped cloth. Again, the disadvantage of the devices disclosed by Weiss and Weiss et al is that construction of the plugs requires a complex and time consuming manufacturing process and such plugs are incompatible with charge assemblies used with projectiles containing guidance elements or other impact sensitive elements.
More recent developments in the art of cartridge case closure plugs are illustrated by the rigid polyurethane foam plug disclosed in U.S. Pat. No. 3,598,058, to Smith. The plug of Smith is a cylindrically shaped polyurethane plug having a density of between 12 and 14.5 pounds per cubic foot after molding. The cylindrical body of the Smith plug is provided with a skirt portion which is adapted for insertion into the mouth of the cartridge case for sealing the propellant bed from the external environment. The disadvantage of using the plug of Smith with projectiles that incorporate guidance systems which are highly sensitive to impact loads is that the high density of the plug results in high impact loads on the projectile which can frequently damage the guidance elements and fin assembly of the projectile.
Additional cartridge case closure plugs have been developed and constructed of high density materials such as 18 pound per cubic foot polyurethane provided with a KEVLAR fiber insert. The fiber insert was necessitated by the tendency of the plug to spall during the process of ramming the projectile and cartridge case into the gun barrel. The disadvantages of the KEVLAR insert plug are, again, the plug requires a complex manufacturing process and, in addition, the high density of the plug material again results in high instantaneous impact loads acting on the projectile which result in damaged guidance elements and damaged fin assemblies.
The present invention of a lightweight, cartridge case closure plug provides a device for effectively sealing the propellant bed of a cartridge case and substantially reduces the impact loads on a projectile which incorporates highly sensitive guidance elements and fin assemblies.